Without special protective measures, transistors can only be actively operated with collector-emitter voltages which lie below a value U.sub.CEO characteristic of the transistors (for example U.sub.CEO =20 volts). In the blocked condition (U.sub.BE =0), however, a higher voltage up to U.sub.CES can be applied to the transistor without damage thereto (for example U.sub.CES =40 volts). Thus the value U.sub.CES is also a transistor characteristic.
The present invention seeks to provide a circuit, in particular a negative-feedback amplifier circuit or voltage controller, which can be actively operated with voltages above U.sub.CEO but below U.sub.CES. The characteristic values or parameters U.sub.CEO and U.sub.CES are determined by the process of manufacture of the transistors as component parts of an integrated circuit. The present invention also seeks to provide a circuit suitable for use in motor vehicles or other applications in which the supply system is subject to high voltage peaks. The invention also seeks to provide an improved circuit suitable for construction by integrated circuit techniques.